Water tube boiler



No v. 18, 1969 J MUNSTER ETAL 3,478,725

WATER TUBE BOILER Filed Sept. 14, 1967 .4 Sheets-Sheet l 62 26 AL 0 F/gJ2B 5 3 76 22 H J.Y T 7 J. MUNSTER ET AL WATER TUBE BOILER Nov. 18, 1969Filed Sept. 14, 196'? .4 Sheets-Sheet 2 In ventosr Nov. 18, 1969 J.MUNSTER ETAL- 3,478,725

WATER TUBE BOILER 4 Sheets-Sheet 5 Filed Sept. 14, 1967 In ventors:

Nov. 18, 1969 U NSTER ETAL WATER TUBE BOILER .4 Sheets-Sheet 4 FiledSept. 14, 1967 Fig.4

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United States Patent 3,478,725 WATER TUBE BOILER Josef Munster,Dusseldorf-Oberkassel, Gerd Wellensiek,

Hosel, and Gunter Linke, Dusseldorf-Urdenbach, Germany, assignors toFerdinand Lentjes Dampfkesseluntl Maschinenbau, Dusseldorf-Oberkassel,Germany, a corporation of Germany Filed Sept. 14, 1967, Ser. No. 667,766Claims priority, application Germany, Sept. 20, 1966,

Int. Cl. uzzb 21 /30 U.S. Cl. 122333 8 Claims ABSTRACT OF THE DISCLOSUREA water tube boiler having a contact heating chamber above a radiationchamber. The water is circulated down through an outer basket ofdowncomer pipes and up through an inner basket of riser pipes bothsurrounding the radiation chamber. At the transition between the twochambers the riser pipes are gathered together and merge continuouslyinto a bundle of tubes extending up the centre of the contact heatingchamber so that the rising gases are confined within a smallercross-section as they flow up through the bundle.

Heating a boiler with a gas under pressure has been known ever since thedevelopment of the Velox boiler. Recently this method of heating hasacquired importance in connection with the partial oxidation of liquidor gaseous fuels, which undergo a chemical transformation during thepartial oxidation and are then cooled by the water circulating in aboiler. The gases being cooled in this way are under a high pressurewhich can be anything between and approximately 120 atmospheres gauge,depending on the nature of the gas and of the process used. However aboiler of the kind mentioned at the beginning can, as an alternative beheated by hot flue gases obtained by normal combustion of liquid orgaseous fuels.

The already known heat exchangers or waste heat recovery boilers areconstructed essentially on the principle of the fire tube boiler. Butthe increasing gas pressures and temperature and the high powerrequirements are making it increasingly difiicult to utilise the gaseseffectively for producing steam. The thermal stresses produced in firetube heat exchangers by the high gas temperatures and pressures arereaching values beyond what the available materials of construction arecapable of withstanding. Heat exchangers of this kind are thereforelimited to comparatively low throughputs of the order of 30,000 Nm./hour and gas pressures of up to 50 atmosphere gauge.

The high gas pressures and temperatures result in particular in veryhigh heat transfer rates near the inlet ends of the heat'transfersurfaces. These high heat transfer rates largely determine the walltemperatures of the structural elements in this region. The inlet gasdistributor in a fire tube boiler must therefore be so designed that thethermal stresses due to the high wall temperatures, and in particularclue to the great temperature difference between the gas side and thewater side of the wall, remain within tolerable limits. A consequence ofthese circumstances is that for a particular material of constructionthere is a corresponding upper limit to the permissible wall thickness,and this in turn determines the size of the distributor, particularlyits diameter, and this limits the power throughput of the heatexchanger. A further difficulty arises from the fact that a fire tubeboiler is sensitive to attack by corrosion, due to the high 3,478,725Patented Nov. 18, 19 69 "ice wall temperatures, particularly by hydrogensulphide, a substance which is often produced by partial oxidation of afuel in the presence of a high concentration of hydrogen. This kind ofcorrosion can be prevented by using expensive chromium steels, but thisremedy has two disadvantages. In the first place it increases the costof the installation and secondly the chromium steels have low heatconductivities and this again increases the wall temperatures and makesstress problems more difficult.

The object of the present invention is to provide a boiler heated bygases under pressure and capable of handling much higher gas throughputsthan have hitherto been possible. In particular the intention is to keepthe temperatures of the materials of construction as low as possibleboth on the gas side and on the water side of the wall, without usingany insulating material, so as to keep the thermal stress problemswithin the limits already prevailing in water tube boiler construction.One of the particular advantages obtained in this way is that the heattransfer materials nowhere reach temperatures so high that it becomesnecessary to use expensive chromium steels to counter corrosive attack.

In contrast to the heat exchangers which have hitherto been developedfor the chemical purposes mentioned at the beginning, the presentinvention is a development from water tube boilers, that is to sayboilers through whose tubes there circulates water or asteam-water'mixture, the heating gases flowing over the outsides of thetubes. The present invention therefore relates to a water tube boilerwith convective or forced circulation of the working medium, and with aradiation chamber through which hot gases pass upwards to a contactheating chamher. The gases will usually enter the radiation chamberunder high pressure and at temperatures above 1200 C.

In accordance with the invention, in such a boiler, the radiationchamber is surrounded by an outer basket of downcomer tubes and an innerbasket of riser tubes which protect the outer basket from radiant heat,the upper parts of the riser tubes being gathered together towards theaxis of the boiler, and merging without any interposed collector into aclosely crowded tube bundle which extends up through the contact heatingchamber and provides surfaces over and through which the gases and theworking fluid both flow in the same direction, the tubes in the bundlebeing so close together that the cross-sectional area of the passageavailable to the flowing gases in the contact heating chamber is lessthan onefifth of the cross-sectional area available to the gases in theradiation chamber.

Although the riser tubes forming the second basket are grouped closelytogether, this is not intended to imply that there is a gastight sealbetween these tubes. On the contrary the tubes should be grouped only soclose together that theyprotect the downcomer tubes of the outer basket,and also the outer pressure vessel itself, from the heat of the gasesunder pressure, which is almost exclusively given off by radiation,while at the same time leaving sufficient gaps between them to allowpressure equalisation between the inner space of the radiation chamberand the annular spaces between the tube baskets and between the outertube basket and the wall of the pressure vessel. It should be observedthat there are no heat insulating materials, in the form of layers ofsubstances having low heat conductivities. Insulation against heat isprovided exclusively by the tube baskets.

In a boiler constructed in this way the inner basket of riser tubesabsorbs the radiant heat in the lower and hotter part of the boiler,where the gases give off heat mainly by radiation, and in this wayprotects the outer basket of downcomer tubes, and also protects thepressure vessel, of the radiant heat. The radiation chamber, throughwhich the gases pass before reaching the convection part of the boiler,cools the heating gases down to 1200 C. or less, before they enter theconvection part. This reduces the heat load near the inlet of theconvection passage, and reduces the temperature of the heat transfermaterial here, at the same time eliminating the risk of H 8 corrosion inthe presence of high concentrations of hydrogen. In the boiler accordingto the invention deposition of soot, coke and other solid impurities onthe convection chamber surfaces is prevented in that the crosssectionalarea of the passage available to the flowing gases decreases in thetransition region between the radiation chamber and the convectionchamber to a small fraction of its previous value, less than one-fifthand even as low as one-fortieth. This constriction in the gas passageincreases the linear speed of the gas by a factor between and 40. It hasbeen found by experience that this increased velocity has aself-cleaning effect which largely prevents deposition of solids.

The diameter of the radiation chamber is determined by the required massrate of flow in the convection part, and by the number of tubes whichare therefore required. This gives the diameter of the radiationchamber, assuming that the tubes are closely grouped together. Thelength of the radiation chamber is determined by the required finaltemperature. In designing the convection part of the boiler, the tubediameter can be increased, compared to what it is in the radiationchamber, so as to shorten the tubes, and thus shorten the enire boiler,for a given heat transfer area.

Preferably the gas passage in the contact heating chamber is subdividedlongitudinally, that is to say in the direction of the tubes, into atleast two separate passages leading to two separate effluent gas outletswhich can be individually shut off. With this arrangement the flow toeither of the two gas passages can be entirely interrupted, with theresult that the velocity of gas flow in the other passage, or passages,is considerably increased, producing a much greater self-cleaningefiect.

In order to provide a wall around the outside of the tube bundle formingthe contact heating chamber it would be posible to install an externaljacket around the tubes. However, the wall may be formed simply bywelding together the outermost tubes of the bundle.

In the contact heating chamber the tubes are crowded very closelytogether, leaving for the passage of the gas hardly more than the sum ofthe geometrical gaps between each three tubes. A narrow passage of thiskind favours heat exchange between the hot gas and the steamwatermixture, but makes it comparatively difiicult for the gases to escapefinally from the tube bundle in radial directions. In order tofacilitate the necessary final escape of the gases, a gas collectorchamber is mounted over the contact heating chamber. Extensions of theriser tubes penetrate through this gas collector chamber and here theexternal diameter of each tube is reduced, com-' pared to what it is inthe convection chamber. In this way larger gaps are obtained between theindividual tubes, allowing the gases to escape sideways quite easilyinto the gas collector chamber.

The construction of the boiler according to the invention is soelfective in preventing deposition of soot, coke and other impurities onthe water tube external surfaces that a mechanical cleaning is necessaryonly after long operational periods, if at all. However, in order toallow mechanical cleaning to be performed, the upper ends of the risertubes may issue into an effluent gas collector chamber which isremovably attached to the boiler, in such a way that after loosening theattachments which hold the collector chamber to the boiler the entiretube system can be lifted clear out of the boiler.

The already known heat exchangers which take heat from partially burntgases are usually connected to their combination chambers by lengths ofpipe. It is a particular advantage of the boiler according to theinvention that no connecting pipes are used here. The boiler can bedirectly attached to the combustion chamber, in which the heating gas isproduced by partial or normal combustion.

One example of a boiler constructed in accordance with the invention isillustrated in the accompanying drawings, in which:

FIGURE 1 is a longitudinal section through the boiler;

FIGURE 2 is a section taken on the line II-II in FIGURE 1;

FIGURE 2a is an enlarged fragmentary view of the tube system as shown inFIG. 2;

FIGURES 2b and 2c are longitudinal views respectively of the mostleft-hand and most right-hand riser tubes of FIG. 2114 showing severalrods for mutually connecting adjacent riser tubes;

FIGURE 3 is a section taken on the line IIIIII in FIGURE 1; and

FIGURE 4 is a section taken on the line IVIV in FIGURE 1.

In the drawing there have been omitted the burner working in thecombustion chamber, the arrangements for supplying the feed water, andthe pipes for taking away the steam. Moreover in FIGURE 1 all the watertubes are represented as single full lines, that is to say not as doublelines. Refractory ceramic material is shown in section cross hatched.

The boiler shown in FIGURE 1 consists of a pressure vessel 6 in the formof an essentially cylindrical steel jacket, the lower end of which isclosed by a hemispherical dome 8 having a flange rem-ovably connectibleby bolts 74 to a corresponding flange 72 on the steel jacket. The upperend is closed by a cover 10 attached by screws to the flange of thepressure vessel. To give an idea of the size of the boiler the diameterof the pressure vessel can, merely by way of example, be approximately 1to 3 m., and the overall length approximately 30 m.

The pressure vessel 6 contains a series of four chambers one above theother. The lower chamber is a combustion chamber 12, which has a bottomopening 13 into which is inserted the burner, which is not shown in thedrawing. The combustion chamber is lined with refractory material 14.When the boiler is operated in the ordinary way, that is to say usingthe usual combustion process, the burner supplies to the combustionchamber compressed air or oxygen together with a gaseous fuel or a fogof liquid fuel. On the other hand, when the boiler is used as a coolerfor a gas decomposed by partial combustion, then there is fed to thecombustion chamber 12 through the burner (not shown) a fog of oil, insteam and oxygen, or alternatively natural gas and oxygen without anysteam.

Above the combustion chamber 12 the pressure vessel 6 contains aradiation chamber 16 into which the normal or partly burnt heating gasflows through a channel 18. The radiation chamber 16 is surrounded bytwo tube baskets, which will be described in greater detail furtherbelow. In the radiation chamber the heating gas gives its heat to thesurroundings mainly by radiation.

Above the radiation chamber 16 the pressure vessel 6 contains aconvection or contact heating chamber 20, which consists of a tubebundle, which will also be described in greater detail further below.The tube 'bundle takes up heat from the heating gas mainly byconvection. The fourth chamber of the boiler is a collector chamber 22and from here the heating gas, which has by now become comparativelycool, leaves the boiler through the pipe connections 24.

The part of the boiler which constitutes the essential core of theinvention is the water tube system. This is connected, in the mannercustomary in water tube boilers, to a drum 26 containing a water space28 and a steam space 30. The water space 28 is connected by a few tubes32 to an annular distributor 34 situated just under a wall 36 made of arefractory material. The wall 36 is a gastight bulkhead separating thegas collector chamber 22 from an annular chamber 54 surrounding theconvection chamber 20. The annular chamber 54 will be mentioned againfurther below. When the boiler is operated with forced watercirculation, a pump is interposed between the drum 26 and the annulardistributor 34. Starting from the annular distributor 34 a number ofdowncomer water tubes 38 extend downwards to near the bottom of thecombustion chamber 12. The downcomer tubes lie clme together close tothe inner surface 40 of the pressure vessel 6, forming the outer tubebasket already mentioned above. At their lower ends the downcomer tubes38 curve around through 180 at 42 to become the riser tubes 44, therebeing as many riser tubes as there are downcomer tubes. From here theriser tubes extend upwards parallel to each other and close together.Where the riser tubes 44 reach the upper end of the radiation chamber 16they all curve over inwards, or are angled inwards, to form a centraltube bundle 46, the tubes here being closely spaced together as shown incross-section in FIGURE 3. A point of great importance in the presentinvention is that there is no collector whatever interposed between theriser tubes in the radiation chamber and those in the convection bundle46, the riser tubes all extending smoothly and without interruption fromtheir lower ends all the way up to where they issue at the top of theboiler. The inclined parts of the riser tubes, where they gathertogether in the region 48 in FIGURE 1, are covered over by a layer 50 ofrefractory material, so that the gases after issuing from the channel 18and passing through the radiation chamber 16 are then compelled to passalong a comparatively constricted passage consisting of the spaceremaining between the tubes of the tube bundle 46. To retain the gaseswithin this constricted passage the tube bundle 46 is sealed off all theway around its periphery. This is done in quite a simple way by weldingiron rods 52 between the outer tubes, one rod between each two tubes, asshown in FIGURE 3. The ion rods extend all the way up the tube bundle.The gases therefore flow upwards inside the tube bundle 46, and no gasesflow through the surrounding annular chamber 54. However, due tounavoidable leakage of gases, an effect which in this case is notundesired, the pressure in the annular chamber 54 is the same as theheating gas pressure inside the tube bundle 46. The temperature in theannular chamber 54 is that of the steam-water mixture in the tubes. Thesteam pressure is usually chosen to' be higher than the pressure of theheating gas, so that heating gas can never leak through into thesteam-water spaces.

At this point it should be mentioned that the riser tubes 44 in theradiation chamber 16 are also connected together by interposed rods 56as shown in FIGS. 2a, 2b and 2c, but only in order to give the tubebasket greater mechanical strength. These rods, that is to say the rods56 in FIGS. 2b and 2c, consist of short lengths of rod attached atintervals.

In order to reduce the length of the pressure vessel the tubes in theconvection part of the boiler have larger diameters than those in theradiation part, as already mentioned above and as represented inFIGURE 1. Above the refractory bulkhead 36 the riser tubes 44 continuein the form of tubes 58 whose external diameters are reduced, comparedto the riser tubes in the convection chamber 20, as represented inFIGURE 4. This is to give more room for radial escape of the heatinggases through the gaps between the tubes. Finally, the tubes 58 issue toa collector 60 which is connected by tubes 62 to the steam space 30 ofthe drum 26, completing the water-steam circuit.

When the boiler is in operation the heating gas flowing from thecombustion chamber 12 into the radiation chamber 16 gives up its heatmainly by radiation to the riser tubes 44 which form the inner tubebasket. The riser tubes absorb this heat and prevent any significantamount from reaching the outer tube basket consisting of the downcomertubes 38, the amount finally reaching the jacket of the pressure vessel6 being very little. During the passage of the gases through theradiation chamber 16 their temperature falls from the initial value ofabout 1800 C. at the inlet down to about 1200 C. The heating gases underpressure tend to deposit soot, coke and other impurities. Thisdifliculty is overcome in the boiler according to the invention in thatat the transition from the radiation chamber 16 to the convectionchamber 20 the cross-sectional area of the passage available to theheating gases decreases at least to one-fifth of its previous value andunder certain circumstances, depending on the type of gas handled and onother conditions, decreases to one-fortieth of its previous value. Thegases flow through the spaces between the riser tubes in the convectionchamber at a greatly increased velocity, and the resulting sustainingefiect ensures that the passages remain almost entirely free fromdeposits. From here the gases pass into the collector chamber 22 andthen issue from the boiler through the pipe connections 24.

For the reasons mentioned at the beginning it is advisable to subdividethe cross-section available to the gases in the convection chamber intoseparate channels. For this purpose the present version of the boilerhas a longitudinal wall which subdivides the convection channel into twohalves. This longitudinal wall is constructed quite simply by weldingtogether a number of tubes near the longitudinal medial plane of thetube bundle, as shown at 64 in FIGURE 3, so as to form a gastightpartition separating the passage for the heating gas into two separatechannels, one for each of the gas outlet connections 24. The partitionis continued in the collecting chamber 22 in the form of a fullseparation bulkhead 66. Outside the boiler, as represented in FIGURE 1,and out beyond the pipe connections 24, there are gas valves 76 allowingone or other of the two gas outlet pipes to be shut off or throttled.When the gases are prevented in this way from escaping through one ofthe gas outlet connections, the velocity of gas flow through the otherhalf of the convection chamber is almost doubled, .with the result thatthe self-cleaning effect is greatly increased. In the versionrepresented in the drawing the convection passage is subdivided into twohalves, but by using more separating walls and more gas outletconnections the passage for the gasesdcan be further subdivided anddifferent elfects produce The riser tubes 44 extend upwards to connectwith a cover 68 which is screwed to the upper part of the boiler.Loosening the screws indicated by centre lines in the drawing, andloosening further connections, allows the cover 10, together with theentire tube system which remains attached to the cover 10, to be liftedupwards right out of the pressure vessel 6, for cleaning and repairpurposes. However in view of the method of functioning of the boiler, asdescribed above, this becomes necessary only after a quite unusuallylong period in service.

We claim:

1. A water tube boiler of the kind comprising means for producingcirculation of the WOI'kirlg medium, a radiat on chamber, a contactheating chamber above said radiation chamber, and means adapted toprovide hot gases for upward passage through said radiation chamber andcontact heating chamber, chracterised in that said radiation chamber issurrounded by an outer basket of downcomer tubes, and an inner basket ofriser tubes in fluid flow communication with said downcomer tubes, atleast an outer layer of said riser tubes incorporating means for forminga substantially gas-tight seal thereabout so as to protect said outerbasket from radiant heat, and in that a closely crowded tube bundleextends up through said contact heating chamber and provides heatexchange surfaces for said gases and working fluid flowing in the samedirection, said riser tubes having portions thereof gathered togetherand merging towards the axis of said contact chamber, said tube bundleextending directly from said portions substantially at and along saidaxis and being so compact as to provide in said contact heating chambera cross sectional area of passage available to said flowing gases lessthan one-fifth of the cross sectional area available to said gaseswithin said radiation chamber.

2. A boiler according to claim 1, characterised by at least oneseparating wall adapted to subdivide said gas passage through saidcontact heating chamber into at least two separate passages, separategas outlets communicating one with with each of said separate passages,and means adapted individually to shut-off said separate gas outlets.

3. A boiler according to claim 1, characterised by means weldingtogether outer tubes of said tube bundle to provide a surrounding wallfor said contact heating chamber to retain said gases in said contactheating chamber.

4. A boiler according to claim 1, characterised by a gas collectorchamber above said contact heating chamber, extension of said risertubes passing therethrough, said extensions having external diametersless than those of said riser tubes in said contact heating chamber.

5. A boiler according to claim 1, characterised by an increase in thediameters of said riser tubes in the region of transition from saidradiation chamber to said contact heating chamber.

6. A boiler according to claim 1, further characterised by an enclosingpressure vessel, a gas tight cover, and means supporting said tubes fromsaid cover whereby said tubes can be lifted with said cover as a unitaryassembly out of said pressure vessel.

7. A boiler according to claim 1, further characterised by a gas inletfor said radiation chamber, a combustion chamber adapted to produceheating gases by partial oxidation or by normal combustion underpressure, and means directly connecting said combustion chamber to saidgas inlet.

8. A boiier according to claim 7, further characterised by meansremovably connecting said combustion chamber to said pressure vessel.

References Cited UNITED STATES PATENTS 2,547,135 4/1951 Mercier 1223332,603,559 7/1952 Patterson 122-333 X 2,672,849 3/1954 Fruit 1223332,672,850 3/1954 Loughin et a1 122--333 FOREIGN PATENTS 806,997 1/1959Great Britain.

CHARLES J. MYHRE, Primary Examiner

